Synthesis, Spectroscopy, and Magnetic Characterization of Copper(II) and Cobalt(II) Complexes with 2-Amino-5-bromopyridine as Ligand

The synthesis, spectroscopic, and magnetic characterization of two new copper(II) and cobalt(II) complexes are described. Both two compounds have the general formula [M(L)2(Cl)2], in which 2-amino-5-bromopyridine. These complexes were prepared in one-step synthesis and characterized by elemental analysis, FTIR, UV-Vis, and EPR spectroscopy. Moreover, the single crystal structure of complex (1) was studied by the X-ray diffraction method. This compound consists of mononuclear units consisting of two ligands linked to metal via the nitrogen of pyridine ring. The UV-Vis spectra of copper(II) and cobalt(II) complexes show three and five absorption bands, respectively, attributed to the d-d transition of the metal ion, ligand → metal charge transfer, and or transitions of the ligand. The FTIR spectra show MN2Cl2 vibrations at 500–300 . The complexes show room temperature magnetic moments of 1.78？BM and 4.12？BM for Cu(II) and Co(II), respectively. The X-band electron spin resonance (ESR) spectra of Cu(II) complex in DMF or DMSO frozen at liquid nitrogen temperature show the typical transition. 1. Introduction The study of transition metal ion complexes by magnetic and optical techniques has furnished a considerable body of empirical data, much of which can be understood in terms of the phenomenological ligand field theory [1]. The major portion of this data is primarily concerned with complexes containing a single paramagnetic transition metal ion; relatively little information is available on dimeric and trimeric coordination complexes [2]. Since copper(II) ions are widely distributed in biological systems, a significant amount of research has centered on the search for relatively simple copper(II) complexes which may display some of the properties of the metalloproteins. One such system of potential importance is that formed by copper(II) halides with pyridine and substituted pyridines [3]. Small low-molecular-weight copper(II) coordination complexes with N-donor ligands have frequently been used to model the active site in copper proteins with the aim of obtaining insight into the correlation between structure and the spectroscopic and magnetic behavior [4–7]. Cobalt(II) complexes are important in biology mainly because of coenzyme B12 [8]. A report of insulin-like action of cobalt(II) chloride implies that such metal complexes may have similarities with vanadium compounds, which exhibit insulin-like effects [9–16]. Electronic properties of cobalt(II) compounds have received substantial attention [17–19] in part due to the fact that many of these complexes